<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>基础应用</title>
</head>

<body>
    <!-- <form method="post"> -->
    <input type="text" id="txt" value="请输入用户名" maxlength="6" />
    <input type="text" id="toggle" value="禁止/取消" disabled />
    <button id="btn">提交</button>
    <button id="toggleBtn">禁止/取消禁止</button>
    <!-- </form> -->
    <script>
        //获取按钮
        var btn = getIdDom("btn");
        //按钮出发点击事件
        btn.onclick = function() {
            //e.preventDefault(); 阻止提交
            var txt = getIdDom("txt");
            //获取value值
            console.log(txt.value);
            //清空value
            txt.value = "";
            //获取焦点
            txt.focus();
        };

        /*
           禁止/取消禁止
        */
        let toggleBtn = getIdDom("toggleBtn");
        let toggle = getIdDom("toggle");
        toggleBtn.onclick = function() {
            toggle.disabled = !toggle.disabled;
        };

        //获取ID方法
        function getIdDom(d) {
            return document.getElementById(d);
        } <
        /body>

        <
        /html>